Conventionally, in the case of performing a cardiac surgery operation of a patient or supporting the cardiopulmonary function, or the like, extracorporeal blood circulation is carried out in which a blood pump of an extracorporeal circulation system is actuated to withdraw blood through a blood removal line (blood removal tube) connected to a vein of the patient so that a gas exchange in the blood is carried out in an oxygenator disposed downstream relative to the blood pump and then this blood is returned to an artery of the patient again through a blood sending line (blood sending tube).
Regarding such an extracorporeal circulation system in which the blood flows in order of the blood removal line, the blood pump, the oxygenator, and the blood sending line, a pressure sensor is conventionally connected to the blood removal line close to the venous side of the patient (see, e.g., Japanese Patent Laid-open No. 2013-192712). Due to this, the blood pressure state of the patient can be determined more correctly. Specifically, for example, it can be envisaged that the amount of blood in the body of the patient is insufficient if the value of the pressure in the tube of the blood removal line is excessively low.
To connect the pressure sensor to the blood removal line as above, generally a method is employed in which a three-way stopcock is connected to the blood removal tube and the pressure sensor is fitted to a connector of this three-way stopcock. Furthermore, in recent years, a device of a type in which a pressure sensor is built into a tube in advance has also existed (see, e.g., Japanese Patent Laid-open No. 2014-68739).